The present invention relates to a fuel adsorption sheet which is arranged downstream of a filter element in an air passage of an air cleaner to adsorb fuel vapor leaking out of an engine air intake system, a method for manufacturing such a fuel adsorption sheet, and an air cleaner employing such a fuel adsorption sheet.
Japanese Laid-Open Patent Publication No. 2003-42017 describes an air cleaner incorporating a fuel adsorption sheet of the prior art. The air cleaner includes a filter element for filtering intake air. The filter element is arranged in a cleaner housing so as to intersect with an air passage. The fuel adsorption sheet, which adsorbs fuel vapor leaking out of an air intake system in an engine, is arranged downstream of the filter element in the air passage so as to intersect with the air passage.
The fuel adsorption sheet has a peripheral portion entirely covered by a resin frame. The resin frame includes a plurality of fastening holes formed in correspondence with the cleaner housing. The resin frame is used to reinforce the entire periphery of the fuel adsorption sheet and to attach the fuel adsorption sheet to the cleaner housing.
However, the fuel adsorption sheet described in Japanese Laid-Open Patent Publication No. 2003-42017 is reinforced only at its peripheral portion. However, the fuel adsorption sheet also includes a central portion in which a fuel adsorption member of activated carbon or the like is arranged. The non-reinforced central portion of the fuel adsorption sheet may be broken by pressure produced when the engine backfires. Furthermore, the non-reinforced central portion of the adsorption sheet easily deforms. Such deformation may cause contact between the central portion and the upstream and adjacent filter element when vibrations are generated during normal operation of the vehicle. This may generate abnormal noise or break the filter element or the central portion of the fuel adsorption sheet. In order to avoid such problems, the filter element must be widely spaced from the fuel adsorption sheet. However, this would increase the size of the entire air cleaner.